There is a device in order to cool an electronic component mounted on a printed wiring board. This cooling device is constituted by being combined a heat sink and fan. The heat sink has a plurality of heat-radiation fins. A cooling device disclosed in Jpn. Appln. KOKAI Publication No. 2001-102787 has a plurality of dividing slits formed in a direction intersecting the heat-radiation fins, in order to enhance the cooling efficiency of the plurality of heat-radiation fins. The dividing slits formed in the heat sink of the cooling device have a length determined in such a manner that part of the heat-radiation fins which are not directly exposed to the flow of air generated by the rotation of a fan are not divided by the slits.
The printed wiring board is cut out in order to arrange a fan or fins of a cooling device inside an electronic apparatus in some cases. Hence, the mounting area of the printed wiring board is reduced by an area corresponding to the cut-out area. It becomes difficult to secure an area to be used to form a new circuit for higher performance and size reduction on the printed wiring board. Further, the heating value of electronic components has been increased with the trend toward higher density of the integrated circuit such as the ball grid array (BGA). It is necessary to employ a large fan or fin with a large heat-radiation area in order to enhance the capability of the cooling device.